If properly configured, an application deployed on GAE platform can leverage HttpSessions to store data between requests. Session data is
stored in the datastore and memcache is also used for speed. Session data is persisted at the end of the request.

The App Engine session implementation will not recognize if properties of objects stored in the session are changed which is why we have
this PhaseListener which will modify a session attribute with the current date and time (in milliseconds) at the end of
every phase.